1. Field of the Invention
The present invention relates to a clutch disk assembly, and more particularly to a clutch disk assembly for use in motor vehicles which have a vibration dampener assembly for taking up torsional vibrations caused by a vehicle engine in the power train.
2. Description of the Prior Art
Clutch disk assemblies for use in motor vehicles are placed in a power train including a gear transmission for transmitting power from a vehicle engine to wheels to drive the motor vehicle. The clutch disk assembly serves to connect and disconnect the power flow from a vehicle engine to the gear transmission, and also to dampen cyclic power pulses or torsional vibrations emanating from the vehicle engine.
Motor vehicles with such clutch disk assemblies have been troubled with the problem of noise produced by the cyclic torsional vibrations from a vehicle engine in coaction with backlash between meshing gears in the gear transmission. For example, when the gear transmission is in a neutral position with the engine running slowly with a small torque, the gear transmission gives off so-called neutral noise due to backlash between intermeshing gears. When the gear transmission is in a high gear (such as when the engine is directly connected to the transmission main shaft) with the engine running at a high speed with a relatively large torque, the gear transmission produces no such neutral noise, but a somewhat confined sound due to high-frequency vibrations.
To neutralize such vibrations, it is necessary for clutch disk assemblies to be equipped with a vibration dampener assembly capable of providing different dampening characteristics that counteract each other. The vibration dampener assembly should have a smaller torsion-resistant rigidity and a smaller dampening resistance. Such a property however fails to suppress the confined sound produced when the engine rotates at a high speed with a relatively large torque. To eliminate the confined sound, the vibration dampener assembly is required to have a greater torsion-resistant ridigity and a larger dampening resistance.
Various clutch disk assemblies have been proposed which have a vibration dampener assembly including spring members, frictional resistance members, and mechanisms for actuating these members for dampening cyclic rotative power pulses emanating from the engine in order to absorb the foregoing vibrations with the different dampening characteristics. Representative examples are disclosed in Japanese Laid-Open Patent Publication No. 113,845 published on Sept. 8, 1981 and U.S. Pat. No. 3,327,820 patented on June 27, 1967.
Each of the diclosed devices is composed of spring members disposed between two members which are rotatable relative to each other, frictional resistance members for presenting a prescribed resistive force to relative rotation of the two members, and a central member for actuating the spring members and the frictional resistance members in a step-like manner dependent on the relative angular displacements of the two members.
The applicant conducted various experiments on the prior clutch disk assembly and confirmed as a result that the disclosed clutch disk assembly was able to neutralize the unwanted torsional vibrations to the extent which is practically acceptable.
However, the applicant also found the following difficulties as a result of the experiments. When a control member made of a thin plate of low rigidity and is used for actuating frictional resistance members which give a relatively small frictional resistive force to absorb the neutral noise, the force exerted on other frictional resistance members for imposing a relatively large frictional resistive force also acts on the frictional resistance members for giving the relatively small frictional resistive force. It then becomes practically difficult for the latter frictional resistance members to impose the desired small frictional resistive force. The frictional resistive force cannot be maintained stable for a long period of time. Stated otherwise, so-called hysteresis cannot be stabilized as plotted on a graphic representation of the relationship between torque and angular displacement when frictional resistive forces are applied.